i break sticks like that from time to time. i think it happens more out of luck than anything else. sometimes you come down at just the right angle that the stick kind of shatters in your hand. rimshots are too fun to not hit them hard. for all the technique questions, it's more a matter of science than technique. basically, no amount of technique can change the fact that wood is softer than metal, hence broken sticks. you could go to a bigger stick, but that might compromise your sound.